The first time a new page is saved the URL is created from the position of the page within the site and the new page title.
For example a new news story might have a default URL of: www.domain.com/news/news-story-title
The Primary URL is the one used by the page.
URLs previously used for the page are automatically saved and redirect to the primary URL.
Manual or vanity URLs can be added that will also redirect to the primary URL.
Click on a row to make it the primary URL for the pageURL changes are automatically saved.